From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 54B06C54E4A for ; Tue, 12 May 2020 09:49:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2CC6D20736 for ; Tue, 12 May 2020 09:49:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589276961; bh=Tck1QbPoKSNuE9nZmTrBvvoOWhkyXgjLULV7ge0ZvIg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=PJwdzrozD7mPKkkk7XYz5TFF11RYBVLxSCrXsgd8GVohuqSV/24HABvzUSzA+dYyF Hld0RG2aY6knBA+Axtg6AhZfpiC/CkCbNd2d8uFOSK2qzrhLkRPIDs8VgMqD+Y17ZR kA9549gdO5W4mY5RrPqdx6rSUjK9b1dJ4s0ZBQh0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729125AbgELJtU (ORCPT ); Tue, 12 May 2020 05:49:20 -0400 Received: from mail.kernel.org ([198.145.29.99]:38752 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725889AbgELJtU (ORCPT ); Tue, 12 May 2020 05:49:20 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8DC6920661; Tue, 12 May 2020 09:49:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589276959; bh=Tck1QbPoKSNuE9nZmTrBvvoOWhkyXgjLULV7ge0ZvIg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Jh+LSg6VPa1MQ6q+ZGZVLbQY+ZBvIal79s0CfMgjL827H0GsZJgsFOs1n3w9OJ5/3 Rsnbie0JyPTEDAX74xpv0pQU6VM+gaTFmjurtsTOBZLRJVmt3GVETJ/l2CgeiE78dk cBnJkMffGIyY7wCbMFRwzFyZCXWWOZmqcGYRUaG4= Date: Tue, 12 May 2020 10:49:15 +0100 From: Will Deacon To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, elver@google.com, tglx@linutronix.de, paulmck@kernel.org, mingo@kernel.org Subject: Re: [PATCH v5 17/18] READ_ONCE: Use data_race() to avoid KCSAN instrumentation Message-ID: <20200512094914.GA3021@willie-the-truck> References: <20200511204150.27858-1-will@kernel.org> <20200511204150.27858-18-will@kernel.org> <20200512082306.GF2978@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200512082306.GF2978@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 12, 2020 at 10:23:06AM +0200, Peter Zijlstra wrote: > On Mon, May 11, 2020 at 09:41:49PM +0100, Will Deacon wrote: > > > + data_race(({ __WRITE_ONCE(*__xp, val); 0; })); \ > > That had me blink for a little, I see how we got there, but urgh. I tried for a while to see if data_race() could act differently if the expression was type-compatible with 'void' and, while I got something that mostly worked, it would fire unexpectedly in a few places where the expression was most definitely not void (e.g. dereferencing a vma pointer) so I gave up :( > Anyway, it's all in *much* better shape now than it was, so no real > copmlaints. Thanks. Will